1. Field of the Invention
This present invention relates to a screening apparatus for separating portions of a mixture of materials having different sizes. More particularly, the present invention relates to a vibratory screening apparatus wherein vibration energy is used to assist the screening action.
2. Background of the Invention
Vibratory screening apparatus are known in the prior art. In one known design of a vibratory screening apparatus, a shaft-driven vibrating mechanism comprises a single shaft which extends horizontally through a screen frame between opposed frame sides in the space between two screen decks. Each end region of the shaft is mounted on the respective screen side through a bearing housing which is secured to the frame side, and a counterweight is mounted on each free end of the shaft which projects outwardly of the respective bearing housing.
Each counterweight comprises an offset mass. Rotation of the shaft results in application of centrifugal force to the shaft through the counterweights which imparts required vibration energy to the screens of the apparatus.
In this known apparatus, substantial bending moments are applied to the shaft by the counterweights, both by reason of the counterweights being mounted on the outwardly projecting ends of the shafts, and also because of the considerable overall length of the shaft which is required to extend throughout the width of the apparatus between the opposed screen frame sides. This causes the mid-region of the shaft to undergo substantial undesirable deflection. The shaft diameter will have to be of a sufficient size to withstand this applied bending load. Also, there will be feedback to the mountings of the bearing housings on the frame sides which will also have to be suitably robust to bear these loads.